Vises have been known in the art as a common means for holding articles in a stationary position while they are being worked on, treated or repaired. For example, such vises are disclosed in U.S. Pat. Nos. 2,313,361 and 4,046,364.
Typically, an article to be held in the vise is placed between a pair of jaws, wherein one of the jaws is stationary and the other jaw is movable relative to the stationary jaw so as to tighten the jaws around the article. However, because articles to be held in the vise are often fragile, it has been difficult with prior art vises to attain the desired degree of jaw closure or clamping force, that is, to tighten the jaws sufficiently to hold the article steady without overtightening and damaging the article.
Several attempts have been made to overcome this problem of overtightening. For example, U.S. Pat. No. 5,110,100 to Cotton discloses a vise designed to prevent excessive clamping force by providing a one-way slip clutch attached to a multi-part shaft. The shaft is positioned between the movable jaw and the drive mechanism for the movable jaw. The clutch is formed from two clutch halves which are biased toward each other.
Another approach for controlling the tightening force of a vise is taught by U.S. Pat. No. 4,046,364 to Coope et al. The vise of this patent utilizes clutch discs which are frictionally loaded against each other so that a predetermined amount of torque is required to cause the discs to slip relative to each other. Like the force control device of Cotton, the Coope et al device requires a multi-part rod or shaft.
Thus, a need exists for a vise having an adjustable closure force control which can be readily adjusted between a closure force limiting mode which prevents the vise jaws from crushing a held article and a direct operating mode which allows the device to operate as a conventional vise. Further, there is a need for an adjustable force control mechanism which can be readily applied to a conventional vise without requiring significant structural modifications of the vise.